Azimuth computer



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I AZIMUTH COMPUTER Original Filed March 20, 1945 2 Sheets-Sheet 2APPROXIMATE SUNS DECLINATION uur 41x14 nl. W

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SHAW/Wto@ -JSEPH H/LSENRATH j/:MUEL G/ BE Patented June 26, 1951 AZIMUTHCOMPUTER Joseph Hilsenrath, Takoma Park, Md., and Samuel Globe,Washington, D. C.

Original application March 20, 1945, Serial No.

583,823. Divided and this application September 19, 1946, Serial No.697,842

(Granted under the act of March 3, 1883, as amended April 30, 1928; 3700. G. 757) 6 Claims.

This application is a division of application Serial No, 583,823, filedMarch 20, 1945, now Patent No. 2,408,776, granted October 8, 1946.

This invention relates generally to navigation instruments, andparticularly to devices for solving spherical triangles.

In the art of navigation it is a constantly recurring problem to solvespherical triangles for one angle when others are known. Compassadjusters must frequently determine azimuth of some celestial body forpurpose or checking the indication of the compass under observation.

It is common practice in such-cases to start with such factors as hourangle, latitude of the observer` and declination of the observed body,and determine its azimuth by reference to various tables, charts, etc. Acompass adjuster will often have a number of azimuth cards or curvescalculated for certain locations.

In these various determinations of azimuth, interpolations are oftennecessary, and the calculations are such that an error early in theprocess may be multiplied as the calculation proceeds, leading to errorsof intolerable magnitude.

At best the calculations are tedious and time consuming. There is a needfor some means for determining azimuths rapidly and with a minimumchance for errors such as are common in the ordinary methods used.

It is, therefore, an object of the invention to provide a simple andpractical device capable of facile and rapid determinations of azimuth,when local app-arent time or hour angle, latitude and declination areknown.

t is an object to provide a device sufficient in A itself for accuratesolution of spherical triangles, avoiding any need for reference tobulky volumes of azimuth tables, etc.

A further object oi our invention is to provide an azimuth computerwhich will give either true or magnetic azimuths.

In the drawings:

Figure l is a representation of a form of this invention, with theprotractor mounted thereon for magnetic or true azimuths.

Figure 2 is a sectional view on line 2-2 of Figure l, and

Figure 3 indicates the back side of the base of the computer.

As indicated in Figure l, our azimuth computer includes an opaque base lon which is printed or otherwise suitably marked a grid 2. The grid iscomposed of hour angle hyperbolas 3 and latitude ellipses 4 in suitableincrements. The line 5,

which we term the axis of the grid, is an axis of 2 the confocalhyperbolas and ellipses, and is parallel to the lower edge of the basel.

Hyperbclas 3 are numbered inside and outside the grid. Latitude ellipsesl are numbered along the axis 5. Since the latitude ellipses also serveto measure declination, the indications along axis 5 are brought downand repeated at scale 6 for convenience in operation.

The dierence in the grids on front and back of the base is only in thescope of latitudes covered. Gn the back are marked ellipses forlatitudes of from 40 to 60, while latitudes of 0 to 45 are marked on theiront side. Front and back grids will be registered so that theprotractor may be used on either side.

Mounted for sliding parallel to the axis 5 is a sliding member i 6 oftransparent material. The lower edge of the sliding member i6 is bentaround the lower edge of the base l to assist in holding the slidinglmember in proper relation to the base l. Pivoted to the sliding mem-berl5 is a protractor "i, also of transparent material, and also pivoted onthis same pivot i 5 is a protractor arm I3. The scale of the protractor'l is indicated at i2. A bolt E with a nut 5J its through a hole insliding member i8 and through an arcuate slot il in the prctractor l,the arcuate slot il being centered on the pivot l5. The bolt 8 extendsthrough and may slide in a slot l0 cut Ythrough base I parallel to the 5and to the bottom edge of the base.

Protractor arm i3 with its index line i4 is pivoted at i5 to the slidingmember i6 in such fashion that pivot i5 lies directly over axis 5 whensliding member it is mounted on the base I. A line Il is marked onsliding' member l5 projecting downwardly from the pivot point I5 forreading against the line 6. Graduations of the protractor 'I arecontinued beyond 0 and 180 on each end of the scale to 20 and 200 asshown. The protractor 'i' may be set to the magnetic variation byreading its scale i2 against the line 5, and secured by tightening thenut 9. If true azimuth is desired, the protractor is secured at theposition of zero variation.

It will be apparent that the sliding member l and protractor 'l may beslid along the base with pivot I5 following axis 5 and that declinationmay be read by consideration ci line il relative to scale 5. Position ofindex line it will be read on suitable scales on the outer edges of theprotractor. In order that the device may be used for north and southlatitudes and for any hour angle or local apparent time, the variousscales Will be suitably numbered and full directions 3 marked explainingoperation. Not all the markings employed are shown to avoid confusingdetail.

The theory of the device is as follows: In the grid', latitude ellipsesl are denned by the equation m2 y2 sec2 l--tan2 Z- Hom` angle hyperbolash are dened by the equation i- 112:1 sin2 h cos2 h,

Systems of latitude ellipses and hour angle hyperbolas are marked on :cand y 'coordinate axes. The intersection of a latitude ellipse with anhour angle hyperbola defines av pointAwhose coordinates are:

Error-nV a pointB on the y axis with coordinates :13:0 y=tan d, whered=declination,

a line AB be drawn, such line will form with the l'J axis an angle awhich represents the azimuth of a body of declination d from latitude Zat hour langle It.

The device described has been designed to solve this systemmechanically. In the grid 2 the line 5 corresponds to the y coordinateaxis.

In operation, to determine azimuth of a given body, with declination,hour angle, and latitude known, the first step is to mount theprotractor on front crback of thebase I, as dictated by latitude. Theprotractor l, set at the desired magnetic variation, and the slidingmember IE, will then be secured by tightening nut c in such posi tionthat line II crosses scale at the proper declination. Arm I3 will thenbe moved to locate line Ifi at the intersection of the eliipse andhyperbola representing the known latitude and hour angle. Line I4 willthen indicate on the scale of the-protractor the azimuth, commonly Lreferred to as Zn.

Inl Figure 1, the instrument is set tov determine true azimuth or zeromagnetic variation when:

Latitude=lll9 Se Declination-:0 I-Iour angle=2h 26m. E.

azimuthrreads on the preti-actor 'I as 48.7?.

If a magnetic variation answer were desired, Vsay 5? Westvariation forinstance, then protractor 'I would be pivoted counterclockwise about itsslot I'I until the 5 W. marking on scale I2 is set on the axis 5 lbeforethe nut 9 -is tightened on the protractor 'I and the sliding member I5.With the same problem set as above, insuch case the 1 factured and usedby or for the Government of e the United States of-America forgovernmental d purposes without the payment of any royalties thereon ortherefor.

What is claimed is:

1. In an azimuth computer, a base member comprising a grid composed ofconfocal hour angle hyperbolas and latitude ellipses, said base memberhaving a plurality of bearing surfaces parallel to the minor axis of theellipses, a sliding member mounted on the base member, said slidingmember having means cooperating with and-engaging said bearing surfaces,whereby said sliding member is slidably but non-rotatably movableparallel to said minor axis, a protractor pivotedfonsaid' slidingmember, at a point coinciding with said minor axis whereby the pivot maymove along said minor axis, pin and slot means offset from said pointlimiting the rotation of said protractor relative to said slidingmember, and an arm pivoted on said protractor at the .same pivot point.

2. In an azimuth computer, a base member comprising a grid composed ofconfocal hour angle hyperbolas andl latitude ellipses, saidv base memberhaving a plurality of bearing surfaces parallel to the minor axis oftheellipses, a sliding member mounted on the base member, said slidingmember having means cooperatingwith and engaging said bearing surfaces,whereby said sliding member is slidably butV non-rotatably movableYparallel to said minor axis, a protractor, pivot meanspivotally'inounting said protrae tor on said sliding member at a pointcoinciding with said minor axis whereby the pivot axis may move alongsaid minor axis, a protractor arm pivoted to said protractor at saidsame pivot point, and means limiting the rotation of said protractorrelative to said sliding member, com prising an arcuate .slot throughsaid protractor and having its center at the axis of said pivot means,and a bearing pin passing through said slot and said base and slidingmembers and including a clamping device for securing the members andprotractor in adjusted relationship.

3. In an azimuth computer, a reversible base member comprising a gridcomposed of confocal hour angle hyperbolas and latitude ellipses,terminating at the minor axis ofthe ellipses, the grid'on one side ofsaid base member being `a continuation of and registered with the gridon the other side thereof, said base member having a plurality ofbearing surfaces parallel to the minor axis of the ellipses, a slidingmember mounted on the base member, said sliding member having meanscooperating with and engaging said bearing surfaces, whereby saidsliding member is slidably but non-rotatably movable parallel to saidminor axis, said bearing surfaces and said cooperating and engagingmeans including an edge on one of said members parallel to said minoraxis and a lip on the other of said members bearing against and engagingwithsaid edge, a protractor pivotally mounted upon said base member withits center upon the minor. axis of said ellipses, a circular slot insaid protractor having the same center as said protractcr, a pin passingthrough said sliding member and said arcuate slot and a cooperating nutto secure said protractor and base member in adjusted relationship, anda protractor arm pivoted to said protractor for movement about itscenter, whereby said sliding member, protractor and arm may be securedon either side of said base member for cooperation withv either grid.

4. In an azimuthA computer, a base member comprising a grid composed ofconfocal hour angle hyperbolas and latitude ellipses, said base memberhaving a plurality of bearing surfaces parallel to the minor axis of theellipses, a sliding member mounted on the base member, said slidingmember having means cooperating with and engaging said bearing surfaces,whereby said sliding member is slidably but non-rotatably movableparallel to said minor axis, a protractor pivoted on said slidingmember, at a point coinciding with said minor axis whereby the pivot maymove along said minor axis, means limiting the rotation of saidprotractor relative to said sliding member, and an arm pivoted on saidprotractor at the same pivot point, said bearing surfaces and saidcooperating and engaging means including an edge on one of said membersparallel to said minor axis and a lip on the other of said membersbearing against and engaging with said edge, and a slot in at least oneof said members and a threaded bearing pin and locking nut in the otherof said members and in said slot, the declination axis being duplicatedbelow the minor axis, an indicator means on said sliding member readingon said duplicate declination axis, an indicator means on saidprotractor arm comprising a line extending from the pivot, saidprotractor being offset between said duplicate declination axis and saidminor axis, said protractor arm being pivoted to the bottom oi saidprotractor between said protractor and said sliding member.

5. In an azimuth computer, a base member comprising a grid composed ofconfocal hour angle hyperbolas and latitude ellipses, said base memberhaving a plurality of bearing surfaces parallel to the minor axis of theellipses, a sliding member mounted on the base member, said slidingmember having means cooperating with and engaging said bearing surfaces,whereby said sliding member is slidably but non-rotatably movableparallel to said minor axis, a protractor pivoted on said slidingmember, at a point coinciding with said minor axis whereby the pivot maymove along said minor axis, means limiting the rotation of saidprotractor relative to said sliding member, and an arm pivoted on saidprotractor at the same pivot point, the declination axis beingduplicated below the minor axis, an indicator means on said slidingmember reading on said duplicate declination axis, an indicator means onsaid protractor arm comprising a line extending from the pivot, saidprotractor being oiiset between said duplicate declination axis and saidminor axis, said protractor arm being pivoted to the bottom of saidprotractor between said protractor and said sliding member.

6. In an azimuth computer, a base member comprising a grid composed ofconfocal hour angle hyperbolas and latitude ellipses; a protractor injuxtaposed relation to said base member, said base member having aplurality of bearing surfaces parallel to the minor axis of the ellipsesand having a straight slot in spaced parallelism with said minor axis; asliding member mounted on the base member and having means cooperatingwith and engaging said bearing surfaces, whereby said sliding member isslidably but non-rotatably movable parallel to said minor axis; aprotractor pivotally mounted upon said sliding member about an axis uponthe minor axis of said ellipses; a circular slot in said protractortangent to the straight slot in said base member and having its centerat the protractor axis of rotation; a pin passing through said slidingmember, said straight slot, and said arcuate slot; a nut cooperatingwith said pin to secure said protractor, sliding member and'base memberin adjusted relationship; and a pro tractor arm pivoted to saidprotractor at the axis of rotation of said protractor upon said slidingmember, whereby said sliding member, protractor and arm may be securedon either side of said base member for cooperation with either grid.

JOSEPH HILSENRATH. SAMUEL GLOBE.

REFERENCES CITED The following references are of record in the iile ofthis patent:

UNITED STATES PATENTS Number Name Date 13,560 Abbott Sept. 11, 18652,408,776 Hilsenrath et al Oct. 8, 1946 2,441,636 Kaufman et al i May18, 1943 FOREIGN PATENTS Number Country Date 537,924 Great Britain July14, 1941 557,901 Great Britain Dec. 9, 1943

